This invention relates to a plastic container, the inner surface of which is coated with a hard carbon film.
In general, plastic containers are widely used as packaging materials in various kinds of fields such as a food field and a medicine field because plastic containers have various benefits which are easy to mold, light in weight and low in cost. However, as is well known, plastic permits low molecular gas, such as oxygen and carbon dioxide, to permeate therethrough, and furthermore, plastic sorbs (i.e., both of absorption and adsorption occur simultaneously) inside therein low molecular organic compound, namely, low molecular organic compound infiltrates into the plastic composition and diffuses therein in such a manner that the low molecular organic compound is absorbed inside the plastic. Therefore, plastic containers are restricted in many aspects to specific objects and forms in use in comparison with other containers such as a glass container.
For example, in case that a carbonated beverage such as beer is filled into a plastic container, oxygen in the atmosphere permeates the wall of the plastic container to reach inside the plastic container, thus gradually oxidizing and deteriorating the beverage contained therein. In addition, carbon dioxide gas in the carbonated beverage permeates, in reverse, the wall of the plastic container and is released off toward outside, thus the carbonated beverage loses its savor.
Further, in case that beverages having aroma component such as orange juice are filled into a plastic container, aroma component (such as limonene in the case of the orange juice) which is a low molecular organic compound is sorbed inside the plastic. Consequently, chemical composition of the aroma components in the beverages may lose its balance to deteriorate the beverages in quality.
In addition, a plastic container may have a problem that low molecular compound contained in the plastic container dissolves in a liquid content contained in the container. More specifically, in case that content (especially, liquid) requiring a high purity is filled into the container, plasticizer, residual monomer or other additives dissolves out of the container into the liquid content, thus deteriorating purity of the content.
Furthermore, at present, how large numbers of used containers are to be treated has become a social issue, and collecting the used containers for the sake of recycling resources is in progress. However, when a used plastic container is to be used as a recycled container, if the used plastic container is left in the environment before being collected, various low molecular organic compounds, such as those producing mold odor, are sorbed in the plastic container, something that does not happen with glass containers. The low molecular organic compounds thus sorbed in the plastic container remain in the plastic even after the container is washed. The sorbed low molecular organic compounds gradually dissolve out of the plastic into the contents of the plastic container as impurities, thereby deteriorating the contents in quality and causing a hygienic problem. As a result, plastic containers can be hardly used as returnable containers, namely, containers collected to be reused.
In order to suppress the above-mentioned features of the plastic, namely, the feature of permitting low molecular gas to permeate therethrough or the feature of sorbing low molecular organic compound therein, crystals in the plastic have been oriented to enhance crystallinity or thin sheets of plastic having a lower sorption or thin films of aluminum have been laminated. In either methods, however, problems of gas barrier property and the sorption of low molecular organic compound cannot be perfectly solved while maintaining the basic properties of the plastic container.
Recently, there has appeared a thin film forming technology for a DLC (Diamond like carbon) film and it is known that laboratory tools such as beakers and flasks are coated with the DLC film. The DLC film comprises amorphous carbon including mainly SP3 bond between carbons. The DLC film is a hard carbon film which is very hard, and has a good insulation, a high index of refraction and a smooth morphology.
Japanese Patent Provisional Publication No. 2-70059 discloses an example in which the DLC film forming technology is applied to laboratory tools for coating thereof. An apparatus for forming the DLC film disclosed in the above publication comprises the followings. As shown in FIG. 16, a cathode 2 is disposed in a reaction chamber 1 having an inlet 1A for carbon resource gas which generates carbon or is converted to carbon and an outlet 1B, and a laboratory tool 3 such as a beaker is accommodated in a space 2A formed in the cathode 2. The reaction chamber 1 is decompressed by discharging air from the outlet 1B after an earthed anode 4 is inserted into an inner space of the laboratory tool 3. After the carbon resource gas is led into the reaction chamber 1 from the inlet 1A, a high frequency is impressed on the cathode 2 from a high frequency power source 5 to excite the carbon resource gas, thus generating plasma to form the DLC film on the surfaces of the laboratory tool 3.
However, in the above DLC film forming apparatus, the reaction chamber 1 accommodates the cathode 2 and the anode 4, so that the volume of the reaction chamber 1 is remarkably large in comparison with that of the laboratory tool 3 to be coated. Therefore, it causes wastes of time and energy for a vacuum operation of the reaction chamber. Furthermore, since the film forming speed (rate) in the above DLC film forming apparatus is 10 to 1000 xc3x85 per minute, which speed is slow, there is a problem in which it is difficult to continuously form the film at a low cost.
The conventional DLC film forming apparatus described above is applied to laboratory tools such as beakers and flasks so as to mainly further increase their qualities, so that the manufacturing cost and time thereof is not much considered. However, containers used for beverages such as beer and orange juice must be manufactured in large quantities at low cost. Accordingly, the DLC film forming apparatus cannot be applied to the containers used for beverages.
In the above DLC film forming apparatus, since the carbon resource gas moves into the space between the inner surface of the cathode 2 and the outer surface of the laboratory tool 3 to be coated, it is impossible to coat only the inner surface of the laboratory tool 3.
Containers for beverages often collide with each other during the manufacturing process in a factory or during the selling process in a store, unlike a laboratory tool such as a beaker or a flask. When a DLC film is formed on the outer surface of a container for beverages, the DLC film itself is damaged by the collisions to decrease the value of merchandise in the containers. Accordingly, it is required that the DLC film is formed only on the inner surface of a container.
It is an object of this invention to provide a plastic container coated with carbon film which can solve the problems of gas barrier property and sorption inherently owned by the plastic while maintaining basic properties of plastic, which can be returnably used to extend the fields and the forms in which plastic containers can be used, which can be continuously manufactured at a low cost, and which is not damaged during handling of the containers.
In order to attain the above object, a plastic container of this invention comprises a bottle for beverages made of a plastic material with a hard carbon film formed only on an inner surface thereof. In addition, the hard carbon film comprises a diamond like carbon film.
According to the above plastic container of the invention, permeability of the container against low molecular inorganic gas such as oxygen and carbon dioxide can be remarkably lowered, and furthermore, the sorption in the plastic of various low molecular organic compounds having a smell can be completely suppressed. The formation of the hard carbon film does not deteriorate the transparency of the plastic container.
The hard carbon film preferably comprises a diamond like carbon film. The diamond like carbon film is a kind of hard carbon film which is called i-carbon film or hydrogenated amorphous carbon film, and is amorphous carbon film mainly including SP3 bond.
Furthermore, the thickness of the diamond like carbon film is preferably within a range of 0.05-5 xcexcm. With the thickness of the diamond like carbon film limited to the above range, adhesive property of the film to plastic material, the durability and transparency and the like of the container can be obtained, and in addition, the sorption in the plastic of low molecular organic compound can be effectively suppressed and gas barrier property of the container can be improved.
The following resins are used as plastic material for containers. Polyethylene resin, polypropylene resin, polystyrene resin, cycloolefine copolymer resin, polyethylene terephthalate resin, polyethylene naphthalate resin, ethylene-(vinyl alcohol) copolymer rein, poly-4-methyl pentene-1 resin, poly (methyl methacrylate) resin, acrylonitrile resin, polyvinyl chloride resin, polyvinylidene chloride resin, styrene-acrylonitrile resin, acrylonitrile-butadien-styrene resin, polyamide resin, polyamideimide resin, polyacetal resin, polycarbonate resin, polybutylene terephthalate resin, ionomer resin, polysulfone resin and polytetra fluoroethylene resin.
Furthermore, the thickness of the diamond like carbon film is preferably within a range of 0.05-5 xcexcm. With the thickness of the diamond like carbon film limited to the above range, adhesive property of the film to plastic material, the durability and transparency and the like of the container can be obtained, and in addition, the sorption in the plastic of low molecular organic compound can be effectively suppressed and gas barrier property of the container can be improved.
The following resins are used as plastic material for containers. Polyethylene resin, polypropylene resin, polystyrene resin, cycloolefine copolymer resin, polyethylene terephthalate resin, polyethylene naphthalate resin, ethylene-(vinyl alcohol) copolymer resin, poly-4-methyl pentene-1 resin, poly (methyl, methacrylate) resin, acrylonitrile resin, polyvinyl chloride resin, polyvinylidene chloride resin, styrene-acrylonitrile resin, acrylonitrile-butadien-styrene resin, polyamide resin, polyamideimide resin, polyacetal resin, polycarbonate resin, polybutylene terephthalate resin, ionomer resin, polysulfone resin and polytetra fluoroethylene resin.
When the plastic container with a hard carbon film formed on an inner surface thereof is applied to a bottle for beverages, the plastic container can be returnably used in place of a conventional glass container.
As described above, the plastic container coated with a hard carbon film of the invention has an excellent gas barrier property and can completely suppress the sorption in the plastic of low molecular organic compound such as odor component, thus making it possible that the container is extensively used as a packaging container in various many fields and as a returnable container capable of refilling therein. Furthermore, since the hard carbon film is formed only on the inner surface of the container in the invention, there is no concern over the damage of the formed hard carbon film during handling of the container.
In case that the hard carbon film formed on the inner surface of the container comprises a diamond like carbon film, the above-mentioned effects become more remarkable.